Civil Engineering Reference
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focus on eliminating hazards and risk factors; administrative solutions such as worker training,
recommended procedures, and job rotation should be considered as solutions only until engineering
changes eliminate worker exposure to hazards can be implemented. Solutions should also be specific.
According to Peterson (2003), “Solutions that merely state, 'Be more alert' or 'Use more caution' or
something similar, are worthless.”
Once the JSA is completed, it is important to make them readily available to workers performing the
job — they do little good if filed in a drawer, which is all to often the case. Also, as the job demands
change (i.e., after a recommended control is implemented), the JSA should be updated. It should be
noted that although quantitative methods may be used to describe risk factors, JSAs do not provide a
quantitative measure of risk factors. Therefore, JSAs alone cannot be used to predict injury, nor can
they alone be used to prioritize tasks. However, JSAs do provide a systematic method to identify
hazards, including MSD risk factors, and to develop potential solutions.
34.4.3.3 Checklists
Many checklists are available as an aid to identify MSD risk factors. Checklists, when used in ergonomics,
are essentially lists of risk factors or workplace conditions that are believed to increase the risk of MSDs.
They help the user to ensure that they have addressed areas of concern, and have not overlooked potential
risk factors. Hence, they are particularly useful for the novice. In general, checklists indicate the presence
of a risk, or if the level of risk is above a certain threshold level (e.g., if the weight lifted is greater
than 20 lbs or if the neck angle is greater than 20
). Consequently, checklists generally do not provide
a quantitative level of risk and, therefore, cannot be used to predict risk of injury.
In their draft ergonomics standard for prevention of work-related MSDs developed in 1995, OSHA
provided a checklist to be used as a screening tool (Schneider, 1995). In addition to indicating the
presence of a risk factor, the tool also assigns a score between 0 and 3, depending on the duration of
worker exposure and the severity of the identified risk factor. The tool is divided into “upper extremity,”
“back and legs,” and “environmental” sections. Score totals are obtained for each section, and then
combined for a total score. A slightly modified version of this MSD Risk Factor Screening Tool is
shown in Table 34.1.
Although the tool has not been validated for its original intended use of providing a threshold value,
the screening tool can provide a relative measure of worker exposure to MSDs. It should also be noted
that interrater reliability is relatively poor, so comparisons made between raters may not be valid. The
numerical score obtained from the screening tool can help prioritize tasks and can also be used to
ensure that risk of injury has been reduced after a design change.
As an example, the tool was used as to provide an assessment of a window assembly task before and
after ergonomic intervention. Figure 34.4 shows the window assembly task being performed before the
ergonomic interventions were implemented. The upper extremity score was 19, the back and legs score
was 6, and the environmental score was 0, for a total score of 25. Ergonomic interventions focusing on
reducing upper extremity MSD risk factors were then implemented. The interventions consisted of: (1)
providing automated screw feeders, (2) using in-line tools, and (3) providing an arm to counteract the
tool torque. The redesigned task is shown in Figure 34.5. The follow-up screening tool analysis score was
11 for upper extremity, 6 for back and legs, and 0 for environmental. Thus, the screening tool indicated
that we have reduced the upper extremity MSD risk factors as intended.
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34.5 Conclusions
In order to get the most from data collected using ergonomic assessment tools, the analysis tool user
must understand some fundamental issues associated with data collection. First, there may be some
intersubject variation in the way tasks are performed, either due to variances in processes or variances
in worker performance. So, it is important to observe the task for a long enough period to account
for these variations. The length of time will depend on the task cycle time and any variation cycles
times. Second, there will also likely be intrasubject variation; work practices can vary between
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